Au nanoparticles have been chemically synthesized and supported in carbon Vulcan XC-72. Using the Au nanoparticles as catalyst, the kinetics and mechanism of the oxygen reduction reaction (ORR), in 0.5 M H(2)SO(4), were analyzed. From rotating disk electrode (RDE) studies, it was found that the number of electrons (n) involved in the ORR depends on the applied potential (E). For E similar to 0.38 V. n was similar to 2, at more negative potentials the value of n increases almost to 4. The kinetic parameters obtained from RDE studies were: -b= 0.110 V dec(-1) and alpha = 0.54. The impedance spectra of Au nanoparticles show one time constant for E> 0.38 V vs. NHE, the time constant was associated to the reduction process from O(2) to H(2)O(2) as the main intermediate. For E < 0.38 V vs. NHE a second time constant appears, and it was associated to the reduction of H(2)O(2) to H(2)O. The values of charge transfer resistance (R(ct1)) obtained from the impedance spectra allows determining the kinetic parameters of the ORR on Au, the Tafel slope (-b= 0.111 V dec(-1)) and charge transfer coefficient (alpha = 0.53) were calculated. The kinetic values b and alpha obtained from ROE and EIS measurements are in good agreement with each other. (C) 2010 Elsevier B.V. All rights reserved.